Synlett 2023; 34(18): 2205-2209
DOI: 10.1055/a-2051-1054
cluster
Modern Boron Chemistry: 60 Years of the Matteson Reaction

Preparation and Use of (γ,γ-Dioxyallyl)boronates

Soshi Nishino
a   Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
,
Yuji Nishii
a   Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
,
Koji Hirano  ∗
a   Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
b   Innovative Catalysis Science Division, Institute for Open and Transdisciplinary Research Initiatives (ICS-OTRI), Osaka University, Suita, Osaka 565-0871, Japan
› Author AffiliationsThis work was supported by the Japan Society for the Promotion of Science (JSPS KAKENHI Grant JP 22J10951, Grant-in-Aid for JSPS Research Fellow to S.N., and JP 22H02077, Grant-in-Aid for Scientific Research(B) to K.H.) as well as by the Japan Science and Technology Agency (JST) FOREST Program (Grant JPMJFR211X to K.H.).
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Abstract

A copper-catalyzed stereoselective 1,4-acylboration of α,β-unsaturated esters with B2pin2 and pivalic anhydride has been developed to afford the corresponding (E)-allylboronates with two distinct oxygenated functionalities at the γ positions, which are difficult to prepare by other means. The chemoselective post functionalizations of Bpin and pivalate moieties in the product are also demonstrated.

Key words

allylboronate - borylation - conjugate addition - copper - stereoselectivity

Supporting Information

    Supporting information for this article is available online at https://doi.org/10.1055/a-2051-1054.
  • Supporting Information


Publication History

Received: 27 February 2023

Accepted after revision: 09 March 2023

Accepted Manuscript online:
09 March 2023

Article published online:
05 April 2023

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  • References and Notes

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  • 8 We also monitored the reaction progress of 1k in toluene-d 8 by 1H NMR spectroscopy, but 2k′ was the primary product under the catalytic conditions: any acyl migration from 2k to 2k′ was not observed. See the Supporting Information for details and a related paper: Zeng L, Lai Z, Cui S. J. Org. Chem. 2018; 83: 14834
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  • 14 Experimental Procedures and Characterization Data Synthesis of 2a (Scheme [4, 0].25 mmol scale) Cu(OAc)2 (4.5 mg, 0.025 mmol), P(3,5-(CF3)2C6H3)3 (33.5 mg, 0.050 mmol), and KOPiv (105.2 mg, 0.75 mmol) were placed in a 20 mL Schlenk tube, which was filled with nitrogen by using the Schlenk technique. CPME (1.0 mL) was then added to the tube, and the suspension was stirred for 15 min at ambient temperature. Bis(pinacolato)diboron (158.7 mg, 0.63 mmol) was then added in one portion, and the resulting solution was stirred at the same temperature. After 5 min, pivalic anhydride (69.8 mg, 0.38 mmol) and methyl (E)-5-phenylpent-2-enoate (1a, 40.5 mg, 0.25 mmol) were added dropwise. The reaction solution was stirred at room temperature for additional 18 h. The resulting mixture was directly filtered through a short pad of neutral alumina and Na2SO4. The filtrate was evaporated in vacuo and purified by silica gel column chromatography on neutral silica gel with hexane/ethyl acetate (20/1 → 10/1, v/v) and GPC (CHCl3) to give 1-methoxy-5-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pent-1-en-1-yl pivalate (2a, 82.5 mg, 0.21 mmol) in 82% yield with >99:1 E/Z ratio. (E)-1-Methoxy-5-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pent-1-en-1-yl pivalate ((E)-2a) 82.5 mg (82%); colorless oil. 1H NMR (400 MHz, CDCl3): δ = 7.27–7.23 (m, 2 H), 7.21–7.19 (m, 2 H), 7.15 (t, J = 7.1 Hz, 1 H), 4.34 (d, J = 9.9 Hz, 1 H), 3.55 (s, 3 H), 2.74 (ddd, J = 13.6, 10.5, 5.4 Hz, 1 H), 2.59 (ddd, J = 13.6, 10.4, 6.0 Hz, 1 H), 2.09–2.03 (m, 1 H), 1.89–1.80 (m, 1 H), 1.73–1.65 (m, 1 H), 1.28 (s, 9 H), 1.25 (s, 12 H). 13C{1H} NMR (100 MHz, CDCl3): δ = 176.5, 150.6, 142.9, 128.7, 128.3, 125.6, 98.2, 83.3, 57.1, 39.1, 35.4, 33.4, 27.2, 24.9, 24.8, 20.5 (br). 11B NMR (128 MHz, CDCl3,): δ = 32.7. HRMS (APCI): m/z [M + H]+ calcd for C23H36BO5: 403.2654; found: 403.2666.
  • 15 We preliminarily tested several reported conditions, including simple heating, Sc(OTf)3 catalyst, and ZnBr2 catalyst, for the allylation of benzaldehyde with 2a, 6, and 7. However, the allylic boronates just decomposed, and the corresponding homoallylic alcohols were not detected at all. Additional investigations are still necessary.
  • 16 We preliminarily tried enantioselective conditions using several chiral phosphine ligands. However, the maximum enantiomeric ratio was 75:25 with a phosphoramidite ligand. See the Supporting Information for more details.